Once you know an atom is protons, neutrons and electrons, describing it is just counting. There are two numbers that do the whole job, and the rest of chemistry leans on them.
The Two Numbers
One — atomic number = the number of protons. This is the big one. The proton count is the atom's name tag: 1 proton is always hydrogen, 6 is always carbon, 79 is always gold. Change it and you've changed which element you have. Nothing else gets a vote. Two — mass number = protons + neutrons added together. Electrons are so light they barely register, so all the weight lives in the nucleus. Add up the protons and neutrons and that's the mass number — roughly how heavy that atom is.
And one rule about electrons: a neutral atom has the same number of electrons as protons. Equal positives and negatives cancel out, so the atom carries no overall charge. Six protons pulling, six electrons answering — balanced, neutral, calm.
The Three-step Method for Any Atom
One — count the protons. That's the atomic number, and it names the element. Look it up: 1 = hydrogen, 2 = helium, 3 = lithium, 6 = carbon, and so on.
Two — add protons and neutrons for the mass number. Protons plus neutrons. Leave the electrons out of this sum — they're too light to count.
Three — check the electrons against the protons. Equal? It's a neutral atom. We'll meet the case where they aren't equal next rung.
A Worked One, Slowly
An atom has 6 protons, 6 neutrons and 6 electrons. Count the protons: 6, so the atomic number is 6 — and 6 protons means it's carbon, no exceptions. Add protons and neutrons for the mass number: 6 + 6 = 12. Check the electrons against the protons: 6 and 6, equal — so it's a neutral carbon atom, mass number 12. Name it from the protons, weigh it with the mass number, check it's neutral. That order works for every atom you'll ever be handed.